In a quantum computer or a quantum storage, a bit is usually a two-level quantum system (quantum bit or “qubit”). The two spin states of a single electron or an other charge carrier have been suggested as quantum bits. However, such quantum bits require the manipulation of an individual electron spin. To this end, local application of magnetic fields to confined electrons is necessary. This requires excellent control of the local magnetic field, since neighboring spins should not be affected by the field.
A very good localization of an applied field results if the field is applied by a magnetic scanning tip. However, this greatly limits the speed with which spins may be manipulated.
Other suggestions for manipulating individual spins include the use of magnetic resonance techniques. In one such approach, a whole device comprising a plurality of quantum bits is flooded in a homogeneous oscillating field slightly off resonance. The individual spin to be manipulated is then displaced into a region where the interactions with the environment are such that the oscillating frequency of the homogenous field is the resonance frequency of the spin. This approach, however, requires the application of high frequency (for electron spins usually in the GHz region) AC magnetic fields. This is technically rather difficult.
Therefore there is a need for a method of manipulating a quantum system with a magnetic moment which overcomes drawbacks of prior art methods and which especially does not require a high frequency AC magnetic field to be applied.
There is also a need for a logic element or a storage element which does not require the application of a high frequency AC magnetic field for a gate operation or writing process.